Propylene resins such as propylene homopolymer, propylene-ethylene block copolymer and propylene-ethylene random copolymer are generally excellent in heat and chemical resistance and moldability and they are cheap. Recently, they have been widely used as materials for molding various containers, domestic electrical products, films, yarns, and interior and exterior automotive trims. Especially for industrial moldings such as a bumper and interior and exterior trims of automobiles, a rubbery elastomer including ethylene-.alpha.-olefin copolymer rubber such as ethylene-propylene rubber and ethylene-butene rubber and a styrene thermoplastic elastomer is incorporated into the polypropylene resin for the purpose of improving an impact resistance of the polypropylene resin. Thereby a polypropylene resin composition is prepared. Thus, the resultant polypropylene resin composition has impact resistance equal to that of the conventional engineering plastic and it has been used as the molding material. For example, U.S. Pat. No. 5,346,964 illustrates a polypropylene resin composition comprising a hydrogenated styrene-butadiene block copolymer.
However, the rubber elastomer has defects since it lowers the stiffness and flowability when its amounts are increased in order to improve the impact resistance of the polypropylene resin. Therefore, in order to obtain a polypropylene resin composition having a good balance between the impact resistance (especially at a lower temperature) and the stiffness, various attempts have been made which have not yet been commercially successful. Moreover, new high melt flow rate polypropylene copolymers have been developed for which the conventional hydrogenated styrene-butadiene or isoprene block copolymer elastomers are ineffective. This invention provides a specific block copolymer modifier for high melt flow rate polypropylene copolymers that allows the production of polypropylene compositions with the desired combination of low temperature toughness, high elongation, and high flow.